Multicoat coating systems are now well known in the coating industry. U.S. Pat. No. 3,639,147 describes such a system for use as an automotive paint. When multicoat coating systems have previously been applied, it has been difficult to obtain coatings having uniformly high gloss while at the same time maintaining good color, and pearlescent features.
In the automotive industry two significant systems are utilized in the painting of automobiles. One topcoat system which utilizes thermoplastic resins is known as the acrylic lacquer system. In this system the base polymers are the homopolymers of methyl methacrylate and copolymers of methyl methacrylate and acrylic acid, methacrylic acid, alkyl esters of acrylic acid or methacrylic acid, vinyl acetate, acrylonitrile, styrene and the like. The acrylic lacquer topcoats have been acknowledged to have outstanding aesthetic properties. Another outstanding topcoat system used in the automotive industry is the thermosetting acrylic resins as described in U.S. Pat. No. 3,375,227, issued Mar. 26, 1968.
These topcoat systems have outstanding chemical resistance, outstanding resistance to cracking and crazing among other outstanding properties, but to the expert paint formulator, the thermosetting acrylic resins have not, in the past, quite provided the aesthetic properties obtained in the acrylic lacquer systems. To overcome the problems associated with the acrylic lacquer topcoats and the thermosetting acrylic resin topcoats, pigmented base coat-clear topcoat multicoat coating systems were developed.
In these systems a pigmented base coat composition is applied to the metal substrate to hide metallic blemishes and provide the aesthetically pleasing colors desired followed by the application of an unpigmented layer of polymer which imparts a "deep" color appearance to the base coat and durability to this pigmented base coat. This system, however, is not without its problems. Aesthetic quality of the coating is totally dependent on the application of the base coat. The clear topcoat magnifies any weakness in this base coat including the highlighting of any color deficiencies of the base coat. The clear coat also acts as a magnifying mirror for ultraviolet radiation which can accelerate rather than retard any degradation of the base coat due to exposure to ultraviolet radiation. In addition, many of these coating systems in use today utilize metal particles in the base coat to provide an aesthetically pleasing metallic appearance. However, problems have occurred with the use of metallic pigments resulting in color loss in the base coat.
In order to overcome the deficiencies of the metallic pigments, pearlescent pigments have been used in the base coat, either with or in place of conventional pigments. Note commonly assigned, copending U.S. patent applications Ser. No. 440,764 filed Nov. 1, 1982, now abandoned and Ser. No. 518,583 filed July 29, 1983, now abandoned. In order to produce novel and improved color effects iron oxide encapsulated mica particles have also been used in a transparent topcoat in a multilayer system. Note commonly assigned copending U.S. patent application Ser. No. 526,724 filed Aug. 26, 1983, now U.S. Pat. No. 4,449,143.
The use of pearlescent pigments produces coating compositions having a metallic-like appearance comparable to, in some respects, conventional metallic pigment coatings. It would be advantageous to produce a multilayer coating wherein the metallic-like appearance is retained while improving the depth, chromaticity, and clarity of the coating.
It is known in the art that the inclusion of dyes in a metallic pigment containing base coat will result initially in improved clarity, chromaticity, and depth. However, these dyes are fugitive in that the dyes tend to fade rapidly upon exposure to ultraviolet radiation. In addition, it is known that metallic flake pigment tends to act as a color reducer and subtracts from chromaticity. That is, an aluminum flake pigment tends to shift the color of a dye or pigment to the gray side or it makes the color look dirty as opposed to being pure.
Accordingly, what is needed in this art are improved coating compositions having a metallic appearance with the advantages of high chromaticity and clarity.